Regulation of gene expression is controlled at the levels of transcription, processing, transport, and mRNA translation. The primary goal of this Section has been to investigate the translational control mechanisms involved in the establishment of translational initiation complexes in eukaryotic cells. Towards this end we have purified and characterized a new translation initiation factor required for the catalytic utilization of eIF-2. We have also clarified the function of this factor (guanine nucleotide exchange) during protein synthesis initiation and have demonstrated its role in the mechanism of inhibition following activation of eIF-2Alpha kinase. The guanine nucleotide regulatory sub-units of eIF-2(Alpha and Beta) have been identified as substrates for ADP-ribosyltrans-ferase purified from turkey erythrocytes, and eIF-4D has been identified as the factor modified by post-translational hypusine formation during lymphocyte growth stimulation. These studies have now been extended towards developing active systems for the in vitro and in vivo transcription of clone eukaryotic genes. Stable transcription initiation complexes have now been isolated for the purification and characterization of the individual factors which regulate expression of RNA polymerase II transcribed genes.